One in five households in the UK were affected by fuel poverty in 2009 official figures showed on Friday with campaigners warning the situation will worsen as electricity and gas prices continue to rise.
The number of UK households in fuel poverty rose from 4.5 million in 2008 to 5.5 million in 2009, the Department of Energy and Climate Change (Decc) figures showed.
The department estimates that the figure was unchanged in 2010 but could rise by 1 million this year. In the UK fuel poverty is when a household spends more than 10 percent of income on fuel for heating, hot water, lights and appliances.
But campaign groups warned that recent price hikes by energy companies will leave millions more people struggling to pay their bills and put vulnerable people at risk.
The figures come a week after the UK's biggest energy supplier announced rises in its gas and electricity prices from August.
Centrica, which owns British Gas, said it was raising its domestic tariffs for gas by an average 18 percent and electricity by an average 16 percent, with some bills increasing by as much as 25 percent.
The company blamed rising wholesale costs, which it said had increased 30 percent since last winter on higher global demand for gas and the impact on supply of unrest in the Arab world.
That announcement comes in the wake of sharp prices rises outlined by Scottish Power, which plans to raise the cost of gas by 19 percent and electricity by 10 percent in August.
It also comes on the back of increases last winter, when British Gas put its charges up by 7 percent in December, adding £1.50 to the average weekly dual fuel bill.
The increases have sparked fears that the rest of the "big six" suppliers will follow suit.
The official consumer group Consumer Focus said the rises could leave as many as 6.4 million households in fuel poverty and called for a comprehensive government strategy to tackle the problem.
It said the average annual gas and electricity bill was currently more than £1,130 but would rise to almost £1,200 when British Gas and Scottish Power increases come in, and could leap further still if other energy companies up their prices.
The new figures show that the majority of fuel poor households in the UK contain "vulnerable" individuals, defined by the government as elderly, disabled, or long-term sick people, or children.
Age UK said almost half the people living in fuel poverty were over 60, and the problem continued to hit the elderly the hardest.
Michelle Mitchell, the charity's director, said: "Research shows many older people are forced to choose between eating and heating their homes, causing illness and in extreme cases, needless deaths.
"These figures should send a clear warning to Government that it is losing the war against fuel poverty and action must be urgently taken to prevent another similar increase next year.
"The only sure way to help people manage rising energy costs is to help them properly insulate their homes and reduce their need for energy -- especially for households in fuel poverty."
Climate change minister Greg Barker blamed the problem on previous Labour government policies.
"I know rising energy prices are hitting households hard," he said.
"These new figures show the old policies to help the most vulnerable were not working."
He said the government's Warm Home Discount will require energy companies to provide discounts of at least £120 to about 600,000 of the poorest pensioners, while a new "green deal" programme will help people save energy, with extra support for the most vulnerable.